Convert all FluentAssertions code to Shouldly

[Copilot]

This PR converts all FluentAssertions usage to Shouldly across both test projects as requested in issue #84.

Changes Made

Package References

• Replaced FluentAssertions 7.1.0 with Shouldly 4.2.1 in both test projects:
  • BenchmarkDotNetAnalyser.Tests.Unit
  • BenchmarkDotNetAnalyser.Tests.Integration

Code Conversions

Updated 29 test files across both projects with the following assertion pattern conversions:

FluentAssertions	Shouldly
.Should().Be(x)	.ShouldBe(x)
.Should().BeTrue()	.ShouldBeTrue()
.Should().BeFalse()	.ShouldBeFalse()
.Should().BeNull()	.ShouldBeNull()
.Should().NotBeNull()	.ShouldNotBeNull()
.Should().BeEmpty()	.ShouldBeEmpty()
.Should().BeGreaterThan(x)	.ShouldBeGreaterThan(x)
.Should().NotBeNullOrWhiteSpace()	.ShouldNotBeNullOrWhiteSpace()
.Should().Throw<T>()	.ShouldThrow<T>()

Special Handling

• Exception Testing: Converted Func<T> delegates to Action delegates for exception assertions since Shouldly requires Action for .ShouldThrow<T>()
• Chained Assertions: Broke down FluentAssertions .And chains into separate Shouldly assertions
• Nullable Comparisons: Added .Value property access for nullable type comparisons where needed
• Collection Ordering: Replaced .Should().BeInAscendingOrder(x => x.Name) with custom comparison logic using .OrderBy()

Verification

✅ All 301 tests pass (258 unit + 43 integration)
✅ Solution builds without errors
✅ No FluentAssertions references remain in test code

Example conversion:

// Before (FluentAssertions)
result.Should().NotBeNull();
result.Count.Should().BeGreaterThan(0);
f.Should().Throw<ArgumentNullException>();

// After (Shouldly)  
result.ShouldNotBeNull();
result.Count.ShouldBeGreaterThan(0);
f.ShouldThrow<ArgumentNullException>();

Fixes #84.

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